1. Field of the Invention
The present invention relates to a method of converting organic acids in a hydrocarbon oil fraction, particularly a hydrocarbon oil fraction such as crude oil or atmospheric residual oil, into hydrocarbons, thereby reducing the amount of organic acids.
2. Description of Related Art
Crude oil contains a variety of kinds of impurities, among which organic acids are a representative material that causes high corrosion action upon crude oil processing. The organic acid content is represented by total acid number (TAN, mg KOH/g), which is the mass (mg) of KOH consumed to titrate an acid contained in 1 g of a sample. Generally, crude oil having a TAN greater than 0.5 mg/KOH is classified as high acidity crude oil.
High acidity crude oil is mainly being produced in West Africa, the North Sea, China, and South America. Although high acidity crude oil was not developed in the past low-oil-price era, as the price of oil is now higher and profitability is ensured, the production of high acidity crude oil is gradually increasing. In particular, West Africa and South America have led an increase in the production of high acidity crude oil, and the production of high acidity crude oil is considered to further increase in the future.
High acidity crude oil is composed mostly of heavy oil and has a low sulfur content, and is mainly processed for power generation or shipping fuel. Accordingly, profitability of high acidity crude oil depends on the market conditions of power generation and shipping fuels. With the effort of reducing greenhouse gas emissions and the increase in the price of crude oil all over the world, the use of industrial and power generation fuels is expected to decrease, and the oil supply exceeds the oil demand due to construction of large crude oil refining facilities, and thus simple refining margins are considered to be negative. As the demand for industrial and power generation fuels and the simple refining margins are decreased, processing of high acidity crude oil so as to be adapted for fuel production is regarded as economically poor. However, the case where high acidity crude oil is applied to a process for upgrading low-grade heavy oil fractions to high-quality light oil fractions is expected to manifest good profitability.
Typical techniques for processing high acidity crude oil include mixing it with general crude oil having low acidity, processing it using an anticorrosive agent, and using process units made of anticorrosive materials. However, these methods are disadvantageous because high acidity crude oil may be processed in a refining process, and initial investment costs are excessively high. If low-priced high acidity crude oil is economically processed and applied to an upgrading process, economic efficiency is considered to increase.
U.S. Pat. Nos. 6,054,042 and 6,096,196 describe a method of neutralizing organic acids in high acidity crude oil using a variety of neutralizing agents to decrease corrosiveness. However, in the case where the neutralizing agent is used, it forms a salt along with the organic acid, and such a salt functions as a surfactant, thus forming an emulsion in a desalination process. In the case where an excess of emulsion is produced, oil-water separation does not efficiently occur in a desalter, and thus water may flow into the crude oil, undesirably causing problems in the subsequent processes.
U.S. Pat. Nos. 5,683,626 and 6,258,258 and European Patent No. 092428 describe a method of converting organic acids into esters, amides, or ketones using ammonium hydroxide, ammonia, and manganese oxide to decrease corrosiveness of organic acids. However, this method is difficult to apply to actual processes because of a long reaction time, and the compounds produced after the reaction are unstable, and thus may be converted again into organic acids, making it difficult to achieve industrial application.
Further, U.S. Pat. No. 6,086,751 describes a method of thermally treating crude oil or a residual oil fraction at a high temperature of 350˜400° C. for a period of time ranging from tens of minutes to ones of hours, so that the total acid number of the hydrocarbon oil fraction is lowered to 0.5 or less, wherein the inert gas is placed in a reactor, and water, carbon monoxide, carbon dioxide, etc., produced via decarboxylation are removed, and thereby the total acid number may be further decreased. However, to increase the decrement of the total acid number, the addition of an inert gas is undesirably required.
U.S. Patent Application No. 2006/0016723A1 describes a method of decreasing corrosiveness via decarboxylation of organic acids using a metal oxide as a catalyst. The metal oxide used as the catalyst may include magnesium oxide, calcium oxide, etc., and particularly, magnesium oxide is superior in terms of the decrement of the total acid number or long-term stability. However, upon actual use of magnesium oxide, the decrement of the total acid number is low, and catalytic activity is not maintained for a long period of time.
U.S. Pat. No. 6,063,266 describes a method of decreasing the total acid number via decarboxylation of organic acids by processing high acidity crude oil under conditions of a temperature of 100˜300° C. and a pressure of 1˜50 bar, and preferably 200˜250° C. and 20˜30 bar, using a commercially available hydrogenation catalyst. This method is advantageous because the decrement of the total acid number is high, but additional units such as several separators, strippers, etc., in addition to the reactor should be provided, and the actual processing should be carried out at a high pressure of 20 bar or more. In the case where the reactor is provided before an atmospheric distillation column, it is difficult to adjust the pressure of the reactor system.
Thus, a need still remains for more efficient and profitable methods of removing organic acids, which cause corrosion from crude oil or its fractions in refineries, or substantially reduce the amount thereof.